Can anyone explain to me why when I send BTC to my blockchain.info I receive it instantly?
You must differentiate between receiving and appearing. Some wallets show transactions after confirmation. [Use of Blockchain.info or others will not change the speed of transaction only fees.]
There is an inverse correlation between Bitcoin transaction Irreversible "double spending" and the number of confirmations.[1]
why do not I need to wait 20 mins for confirmations?
You do not need twenty minutes, the time of confirmation varies depending on the fee and mempool [check [2] or [3]*].
[1]
https://en.bitcoin.it/wiki/Irreversible_Transactions[2]
https://core.jochen-hoenicke.de/queue/#24h[3]
https://bitcoinfees.earn.com/ * Not accurate